HEKA Elektronik EPC 10 USB, Руководство по оборудованию, Страница: 30 / 81

24 Verifying and Testing the EPC 10 USB
4.1.6 Measuring the Noise of the Amplifier
Now let us come to the final section of the tutorial and check the intrinsic noise of the amplifier.
Patchmaster
has a built in feature that allows you to easily and quickly check the noise of your amplifier and to minimize your
setup’s noise, e.g., by optimizing the grounding of the setup. First, remove anything from the probe and shield
its input with the metallic cap. It is recommended to click the
Reset button in the Amplifier window in order to
reset the
EPC 10 USB
to its initial default configuration. Now click the Noise button (1) to start the noise test.
In the Noise test mode no stimulation will occur. Instead,
Patchmaster
will calculate the noise of the current
monitor 2 (Imon2) and display it in (2). Select the highest feedback resistor of the pre-amplifier, which has the
lowest intrinsic noise by switching into a gain of 50 mV/pA or higher (3).
Note: The three different Gain ranges of the
EPC 10 USB
are separated by lines in the Gain pop up
menu. The low Gain range goes from 0.005 to 0.2, the medium Gain range from 0.5 to 20 and the high
Gain range from 50 to 2000 mV/pA.
Note: Because of poor dielectric properties in the internal switch, the model circuit introduces excess
random noise above the level that can be obtained with a gigaseal.
The action of the internal filters on the background noise level and the temporal response can be observed by
changing
Filter 1 (4) and Filter 2 (5). An improved signal-to-noise ratio should be apparent when the Gain is
increased to 50 mV/pA or greater (which selects the 50 G Ω measuring resistor). With Filter 2 set to 2.9 kHz (5)
and nothing attached to the probe you should read a noise value below 110 fA (2).
Figure 4.7: Noise measurement
Tip: If you wish to ground your setup you should now attach the pipette holder to the probe, insert a
glass pipette, bring the pipette tip into the recording position near the recording chamber and power on
every piece of equipment that introduces noise (lamps, oscilloscope, camera, . . . ). Setting the duration
of the
Test Pulse to 100 ms (6) and the Gain (3) of the
Patchmaster
Oscilloscope to a high value will
make the noise and the 50/60 Hz pickup very obvious. In a well grounded setup all these components
should introduce no more than about 100 fA of additional noise.
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